The present invention relates to solar energy and, specifically, to creating energy from solar radiation utilizing nanowire structures.
A solar cell or photovoltaic cell is a device that converts solar energy into electricity by the photovoltaic effect. Photovoltaic electricity generation is one of the most promising sources of alternative energy. Accordingly, research and development in this area is important and may yield viable alternatives to current energy sources.
Currently, one type of photovoltaic device showing good efficiency are multijunction solar cells based on type III-V semiconductor technology. These cells achieve their high efficiency by combining several solar cells, or p-n junctions, into a multijunction cell and include multiple subcells. Each of these subcells is composed of a different semiconductor material having a bandgap of different width. Typically, each cell has a three-junction cell configuration with three-subcells electrically connected in series. The subcells are also positioned in optical series such that the subcell with the largest bandgap is on top (facing the sun) and the other subcells are positioned in order of descending width of the bandgap. Hence, in the top subcell only the photons with the highest energy are absorbed. Photons with a lower energy are transmitted to the subcell beneath, and so on. In this way the multijunction solar cell divides the broad solar spectrum into wavelength bands, each of which can be used more efficiently by the individual subcells than in a single-junction case. In particular, photons with higher energy contribute with a larger photo-voltage than those with lower energy. Multijunction solar cells require a tunnel diode for current transfer from one subcell to the other. State-of-the-art multijunction cells provide an energy conversion efficiency of 40%.